A mysterious cloud caused a stir over Perth this morning. Several PerthNow readers have woken to a sight described as "out of this world" after spotting a puzzling UFO-shaped cloud in the sky.The unusual cloud formation even had experts baffled, with the Bureau of Meteorology taking some time to investigate what the strange phenomenon may be.

Anyone fearing an alien invasion can now have their minds put at rest as experts at the Bureau of Meteorology have confirmed their original suspicions are true - the strange phenomenon sighted in Perth skies this morning was in fact a Fallstreak Cloud. As aircraft flew through the cloud, the particles in their jet exhaust caused this extremely cold water to instantly freeze. The newly frozen ice crystals inside the cloud became a lot heavier then the cloud itself.As a result, the heavier ice crystals fell through the cloud, leaving an usual hole - just like the one Perth locals reported seeing this morning. A Fallstreak hole is a cloud formation that gives the appearance of strange holes in the sky's cloud layer.